This invention relates to an apparatus for moving and assembling magnetic members using a combination of permanent magnets and electromagnets. More particularly, the invention uses a movable electromagnet to selectively engage and disengage from a permanent magnet member and to use the permanent magnet both to pick up and move one part into engagement with another and to leave the permanent magnet engaged with the parts to serve as a magnetic clamp.
A particular application for the invention is in the assembly of refrigeration cabinets, where the wall surfaces are used as a heat exchanger for the condenser or evaporator, or both. In the case of food freezers, the outer wall or shell and the inner wall or liner are each cut and punched as necesssary, as generally flat sheets, with all of the wall surfaces in a plane. The tubing for the condenser or evaporator is performed in a tube bending apparatus into a serpentine arrangement generally in accordance with the configuration of tubing is to have when attached to the respective sheet. In the assembly procedures used heretofore, the serpentine is placed loosely on top of the sheet and then moved into final position by sliding the tubing along the surface of the sheet until the exact position is obtained. At this point, the tubing is attached to the sheet by various means such as straps covering the tubing and welded directly to the sheet, or by spot-welding the tube directly to the sheet. With this method of assembly, it is not necessary to have the serpentine arrangement assume the exact configuration prior to assembly, because it is possible to slide it around the sheet as desired, since the tubing is generally quite flexible, and if the tubing has been accidentally somewhat deformed during or after the serpentine bending process, it is easily held in place during the fastening operation without problems. Using this procedure, after the tubing has been held in place, the tubing and walls can be folded along seams into the walls of a box. Prior to complete assembly of the cabinet, it has been customary, to improve the efficiency of operation, to apply a thermal mastic having a high thermal conductivity to the tubing and the adjacent portions of the sheet to improve the thermal transfer from the tubing to the sheet for maximum exchanger efficiency.
According to an assembly procedure as disclosed in copending U.S. patent application Ser. No. 080,750, filed July 31, 1987, assigned to the assignee of this invention and incorporated herein by reference, it has been found that greater efficiency and economy in use of thermal mastic are obtained by first applying beads of thermal mastic to the panel at the location where the tubing serpentine is to be placed, and after the thermal mastic is in place, the tubing is then brought into contact with the sheet. This procedure does not allow any movement of the tubing after it is in contact with the sheet, and therefore it is necessary to hold the tubing in the precise configuration in which it is to be assembled and, while holding it in this configuration, it is moved directly into contact with the sheet in the finished configuration. After this has been done, it is necessary to clamp and hold the tubing serpentine in the same configuration on the sheet until the fastening operation, in the above-mentioned application the application of hot melt adhesive on top of the tubing and sheet, has been completed, after which it is then necessary to unclamp the tubing and leave it free to be folded with the sheet into the finished wall configuration.